Abstract: A18.00003 : On the dynamics of Reynolds stresses in the tip region of axial turbomachines*

Authors:

Huang Chen(The Johns Hopkins University)

Yuanchao Li(Johns Hopkins University)

David Tan(Johns Hopkins University)

Joseph Katz(Johns Hopkins University)

Experiments examining the flow in the tip regions of axial turbomachines
have been performed in a refractive index matched facility, enabling
unobstructed optical access. Stereo PIV measurements in closely spaced
planes provide high-resolution 3D distributions of the strain rate and
Reynolds stress tensors in the rotor passage. In areas dominated by large
vortical structures, such as the tip leakage vortex (TLV) and the backflow
vortex that propagates circumferentially, the strain and Reynolds stress
tensors are poorly correlated, and the measured eddy viscosity fluctuates
from large negative to positive values. In the vortex cores, a substantial
fraction of the unsteady motion involves large-scale structures. The
turbulence is highly anisotropic and inhomogeneous, with an anisotropy
tensor shifting from 1D to 2D to 3D over small distances. Ingestion of
turbulence across the tip gap enhances the turbulence production and
increases the Reynolds stresses substantially. However, the distributions of
Reynolds stresses depend on their history, hence affected by advection and
diffusion in addition to local production and dissipation rates. The TLV
breaks up in the aft part of the passage generating a broad area with
elevated turbulence, but with lower peak values.